1. Field of the Invention
The present invention relates to an in-vehicle apparatus remote control system and an in-vehicle apparatus remote control method for performing code comparison through communication with a mobile apparatus and controlling permission of the usage of a vehicle, based on the result of the comparison.
2. Description of the Related Art
To date, in addition to a remote operation function of manipulating the operation unit of a mobile apparatus so as to lock or unlock the door keys of a vehicle, there has been a smart entry system in which, without manipulating the operation unit, a return code signal is transmitted in response to a transmission request signal from the vehicle and the code is compared, so that the door keys are locked or unlocked.
For example, Patent Document 1 (Japanese Patent Laid-Open No. 1993-106376) discloses a keyless entry system (i.e., a smart entry system) configured with a mobile wireless apparatus provided with a first transmission means that transmits a response signal when a first reception means receives a calling signal and an in-vehicle wireless apparatus provided with a control means that outputs a signal for unlocking the door keys of a vehicle when a second reception means receives the response signal that is transmitted after the calling signal transmitted at a predetermined interval from a second transmission means has been received, and that outputs a signal for locking the door keys of the vehicle when the second reception means receives no response signal.
Additionally, to date, there has been a smart start system that makes it possible to perform engine start operation without utilizing any mechanical key, by transmitting a return code signal in response to a transmission request signal from a vehicle and comparing the code, thereby unlocking a steering lock mechanism and releasing the operation of an engine start prohibition device.
For example, Patent Document 2 (Japanese Patent Laid-Open No. 1988-1765) discloses an ignition system (i.e., a smart start system) configured with respective means that permit unlocking operation for the steering lock mechanism, switching operation for the engine switch, and switching operation for the accessory switch, when a calling signal is transmitted to a mobile wireless apparatus, a PIN code is received and compared with an internal code, and they coincide with each other.
In addition, a system in which the foregoing smart entry system and smart start system are combined is referred to as a smart entry/start system.
In a smart entry/start system, the responsiveness to manual operations, such as foregoing door-key locking and unlocking and key-cylinder unlocking, is an important performance.
One of the problems is how to shorten communication time for code verification so as to reduce response time.
For example, Patent Document 3 (Japanese Patent Laid-Open No. 1997-144411) discloses that, in a keyless entry system in which, while a receiver provided in a vehicle transmits a search signal for searching for a mobile transmitter, a transmitter transmits an ID code signal which is set for each transmitter, in response to the reception of the search signal, and then in the case where the ID code signal received by the receiver provided in the vehicle coincides with an ID code signal set for the vehicle, the door keys are unlocked, the transmitter has a transmission means for transmitting the ID code signal after a preset delay time from the reception of the search signal transmitted from the vehicle.
As described above, in the conventional keyless entry system disclosed in Patent Document 3, the communication between the receiver provided in a vehicle and a plurality of mobile transmitters is performed in accordance with the time-slot method; therefore, the more the transmitters (i.e., mobile apparatuses) are, the more time the communication takes.
In contrast, Patent Document 4 (National Publication of International Patent Application No. 2003-500957) discloses a remote access control method, which is a method of controlling remote access by use of an apparatus provided with a transceiver unit, in which the transceiver unit transmits a polling signal for simultaneously activating all access code generators; after that, all the access code generators that receive the polling signal substantially concurrently transmit respective inherent access code signals; and the transceiver unit performs separation of the access code signals that are simultaneously received, based on respective features added on the access code signal. Moreover, Patent Document 4 describes that, in the process of the communication between the in-vehicle unit and the access code generators to respond, the access code generators are made to respond by means of a single common polling signal; the access code generators respond temporally in parallel; and respective features that enable temporally parallel processing in the in-vehicle unit are added on the transmission signals through modulation.
In other words, in Patent Document 4, a spread-spectrum communication method is proposed which is capable of multiple access and in which communication time is constant regardless of the number of transmitters (mobile apparatuses)
However, the communication method according to the foregoing proposal requires as many kinds of PN codes (pseudo-noise code, i.e., pseudorandom signal) as the number of mobile apparatuses (=the number of vehicles produced×the number of mobile apparatuses/vehicle).
Accordingly, the PN code with sufficiently long code length is required; for example, in order to prepare approximately one thousand kinds of balanced GOLD codes in which the cross-correlation between codes are low and the number of occurrences of “1” is balanced with that of “−1”, the code length is required to be 225 bits (chip).
In addition, because a first reception means requires as many correlators as the number of mobile apparatuses, the circuit scale becomes large and the production cost is raised.
In contrast, as a method in which the length of the PN code is shortened and the number of correlators is reduced, a method is well known in which identical PN codes whose phases are different by more than one chip from one another are utilized as independent PN codes; for example, as proposed in Patent Document 5 (Japanese Patent Laid-Open No. 1994-244821), there exists a method in which PN codes are multiplexed.
However, as described later, in the smart entry/start system, an LF-band electric wave (typically, 125 KHz) is utilized for the communication between the first transmission means in an vehicle and the second reception means in a mobile apparatus; a UHF-band electric wave (typically, 315 MHz) is utilized for the communication between the first reception means in an vehicle and the second transmission means in a mobile apparatus.
Although, in order to realize the foregoing phrase difference of more than one chip, management accuracy on the order of one microsecond is required, the reception timing, of the second reception means, which determines the transmission timing of the second transmission means cannot be managed with accuracy of less than approximately several wave lengths (several tens of microseconds) of a utilized LF-band radio wave, due to variations in the mobile apparatuses and the distances from the transmission antenna.
Accordingly, it is difficult to securely prevent communication collisions (communication interferences) among the mobile apparatuses; thus, unless further measures are taken, the reliability of the proposal in Patent Document 5 is low, and the multiplexing utilizing the phase difference is not feasible.
Expanding the length of the PN code in such an extent as to enable the temporal management causes the deterioration of the communication speed and the scale enlargement of the correlator; therefore, this method is not desirable in terms of a system.
As described above, in the conventional keyless entry system disclosed in Japanese Patent Laid-Open No. 1997-144411, the communication between the receiver provided in a vehicle and a plurality of mobile transmitters is performed in accordance with the time-slot method; therefore, the more the transmitters (mobile apparatuses) are, the more time the communication takes.
Additionally, the conventional technology (remote access control method) disclosed in National Publication of International Patent Application No. 2003-500957 requires PN codes in the number corresponding to the number of the mobile apparatuses; therefore, the length of the PN code is considerably long and the reception means in a vehicle requires as many correlators as the number of the mobile apparatuses, whereby the circuit scale is enlarged and the production cost is raised.
Additionally, it is difficult for “the method of multiplexing utilizing spread spectrum communication system” disclosed in Japanese Patent Laid-Open No. 1994-244821 to securely prevent communication collision among the mobile apparatuses; thus the reliability of the communication is low.